RESUMO
HP1 proteins are transcriptional regulators that, like histones, are targets for post-translational modifications defining an HP1-mediated subcode. HP1γ has multiple phosphorylation sites, including serine 83 (S83) that marks it to sites of active transcription. In a guinea pig model for Shigella enterocolitis, we observed that the defective type III secretion mxiD Shigella flexneri strain caused more HP1γ phosphorylation in the colon than the wild-type strain. Shigella interferes with HP1 phosphorylation by injecting the phospholyase OspF. This effector interacts with HP1γ and alters its phosphorylation at S83 by inactivating ERK and consequently MSK1, a downstream kinase. MSK1 that here arises as a novel HP1γ kinase, phosphorylates HP1γ at S83 in the context of an MSK1-HP1γ complex, and thereby favors its accumulation on its target genes. Genome-wide transcriptome analysis reveals that this mechanism is linked to up-regulation of proliferative gene and fine-tuning of immune gene expression. Thus, in addition to histones, bacteria control host transcription by modulating the activity of HP1 proteins, with potential implications in transcriptional reprogramming at the mucosal barrier.
Assuntos
Proteínas da Membrana Bacteriana Externa/metabolismo , Carbono-Oxigênio Liases/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Disenteria Bacilar/metabolismo , Enterocolite/metabolismo , Shigella flexneri/metabolismo , Transcriptoma , Animais , Proteínas da Membrana Bacteriana Externa/genética , Carbono-Oxigênio Liases/genética , Células Cultivadas , Homólogo 5 da Proteína Cromobox , Proteínas Cromossômicas não Histona/genética , Modelos Animais de Doenças , Disenteria Bacilar/genética , Disenteria Bacilar/patologia , Enterocolite/genética , Enterocolite/patologia , MAP Quinases Reguladas por Sinal Extracelular/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Estudo de Associação Genômica Ampla , Cobaias , Camundongos , Camundongos Mutantes , Fosforilação , Proteínas Quinases S6 Ribossômicas 90-kDa/genética , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Shigella flexneri/genéticaRESUMO
Shigella flexneri, a gram-negative bacterium responsible of bacillary dysentery, uses multiple strategies to overcome host immune defense. We have decrypted how this bacterium manipulates host-cell chromatin binders to take control of immune gene expression. We found that OspF, an injected virulence factor previously identified as a repressor of immune gene expression, targets the chromatin reader HP1γ. Heterochromatin Protein 1 family members specifically recognize and bind histone H3 methylated at Lys 9. Although initially identified as chromatin-associated transcriptional silencers in heterochromatin, their location in euchromatin indicates an active role in gene expression. Notably, HP1γ phosphorylation at Serine 83 defines a subpopulation exclusively located to euchromatin, targeted to the site of transcriptional elongation. We showed that OspF directly interacts with HP1γ, and causes HP1 dephosphorylation, suggesting a model in which this virulence effector "uses" HP1 proteins as beacons to target and repress immune gene expression (Harouz, et al. EMBO J (2014)). OspF alters HP1γ phosphorylation mainly by inactivating the Erk-activated kinase MSK1, spotlighting it as a new HP1 kinase. In vivo, infectious stresses trigger HP1γ phosphorylation in the colon, principally in the lamina propria and the intestinal crypts. Several lines of evidence suggest that HP1 proteins are modified as extensively as histones, and decrypting the impact of these HP1 post-translational modifications on their transcriptional activities in vivo will be the next challenges to be taken up.